All good advice here, care, but don't worry about this one. Do bear in mind that in addition to the good advice here, when flying aircraft larger than the great 150, if you are climbing for prolonged periods at an airspeed low enough to chirp the stall warning, you may not be allowing the engine cooling which would be optimum. Lower the nose a little when the obsticles are cleared.
Go up high with an insructor and practice slow flight in the 150, it is amazing. With full flaps you can fly power on with the stall horn screaming and still be very safe - key words: High & Instructor.
The stall warning horn on the 150 acts as air is sucked out through it. Other aircraft types have a vane, which is actually a switch. The switch type is either on or off, or chirping in between. The 150 type is more akin to a musical instrument, and it's intensity will increase as the situation worsens. Tune your ear and go try it - high & instructor. You will learn that the first low tone is just the beginning of the fun.
Pilot DAR